Molded articles of crystalline poly (ethylene/alkylene) terephthalates which crystallize rapidly

ABSTRACT

Terephthalic copolyesters, the diol component of which consists of ethylene glycol and 2.2-diethyl propane-1.3-diol crystallize more rapidly than pure polyethylene terephthalate and can be molded in a way comparable to butylene terephthalate.

This application is a continuation-in-part application of ourapplication Ser. No. 658,816, filed Feb. 17, 1976 now U.S. Pat. No.4,086,212 granted Apr. 25, 1978.

The present invention relates to molded articles of highly crystalline,thermoplastic copolyesters which crystallize rapidly and which are basedon terephthalic acid radicals, ethylene glycol radicals and 2.2-diethylpropane-1.3-diol radicals.

Polyalkylene terephthalates have achieved considerable importance as rawmaterials for the preparation of fibres, films and moldings. By reasonof their partially crystalline structure, they possess outstandingproperties, such as high wear resistance, favorable crrep properties andhigh dimensional accuracy, and are therefore particularly suitable forthe production of moldings which are subjected to severe mechanicalstress and exposed to severe heat. An additional improvement in themechanical properties can be achieved by the incorporation ofreinforcing materials, for example glass fibres (GB Patent SpecificationNo. 1,111,012, U.S. Patent Specification No. 3,368,995 and DT-AS(GermanPublished Specification) No. 2,042,447).

Because of its particular physical properties, polyethyleneterephthalate is suitable especially for the production of fibreproducts and films. However, for the preparation of moldings, thenecessity for high mold temperatures (about 140° C.), and relativelylong pressing times is a disadvantage which is only partiallycompensated by exceptional rigidity and a high heat distortion point.

Although polypropylene terephthalate and polybutylene terephthalaterequire shorter pressing times and lower mold temperatures (about 100°C.) than polyethylene terephthalate, since they crystallize considerablymore rapidly, they have poorer physical properties, in particular alower heat distortion point, compared with polyethylene terephthalate.

There has been no lack of attempts to provide polycondensates in whichthe good properties of both polyethylene terephthalate and polypropyleneterephthalate or polybutylene terephthalate are combined. Thus it isknown, for example, that the tendency of polyethylene terephthalate tocrystallize can be improved by nucleation with suitable nucleatingagents and/or by increasing the rate of diffusion within the melt byadding lubricants (compare K.-D. Asmus in Kunststoff-Handbuch (PlasticsHandbook) volume VIII, "Polyester" ("Polyesters"), page 697 et seq.,Carl Hanser Verlag, Munich 1973). However, these measures are notsuitable for increasing the rate of crystallization of polyethyleneterephthalate to such an extent that it can be processed at low moldtemperatures and short molding times similar to those used in the caseof polybutylene terephthalate.

It is known from DT-OS(German Published Specification) No. 2,349,396that it is possible to blend polybutylene terephthalate withpolyethylene terephthalate or to replace 1 - 20 mol% of thebutane-1,4-diol units of the polybutylene terephthalate by ethyleneglycol units without a substantial reduction, or even with an increase,in the rate of crystallization. This result would be the more surprisingsince it is known that the rate of crystallization is reduced withlinear polyesters are modified by codiols (compare R. E. Wilfong, J.Polym. Sci. 54, 385 (1961); L. Mandelkern, "Crystallization ofPolymers", McGraw-Hill Inc., New York 1964; P. I. Flory, Trans. FaradaySoc. 51, 848 (1955); and R. K. Eby, J. Appl. Physics 34, 2442 (1963));however, we were not able to reproduce the results of DT-OS 2,349,396 byexperimental checking. Accordingly, in agreement with generally acceptedteaching, it appeared to be impossible to improve the rate ofcrystallization of linear polyesters by incorporating comonomers. As isknown, codiols with one or more branch points, which display a markedcrystallization-inhibiting effect, such as, for example, 2-substitutedpropane-1,3-diols (compare GB Patent Specification No. 1,268,442) areused to prepare amorphous polycondensates.

It has now been found, surprisingly, that the tendency of polyethyleneterephthalates to crystallize is not reduced by modification with2.2-diethyl propane-1.3-diol radicals but, on the contrary, isdistinctly increased so that the polyethylene terephthalates modifiedaccording to the invention have a rate of crystallization comparable tothat of polybutylene terephthalate.

The subject of the present invention are, then, molded articles ofhighly crystalline, thermoplastic terephthalic acid copolyesters whichcrystallize rapidly and which consist of at least 90 mol %, relative tothe dicarboxylic acid component, of terephthalic acid radicals, 95.2 to99.5 mol %, relative to the diol component, of ethylene glycol radicalsand 0.5 to 4.8 mol %, relative to the diol component, of 2.2-diethylpropane-1.3-diol radicals.

The polycondensates according to the invention crystallize considerablymore rapidly than pure polyethylene terephthalate and possess a veryhigh melting point, that is to say a combination of properties which ishighly desirable and which has not been achieved by the terephthalicacid esters known hitherto.

In addition to terephthalic acid radicals, the polyesters according tothe invention can contain up to 10 mol %, relative to the acidcomponent, of radicals of other aromatic or aliphatic dicarboxylic acidssuch as, for example, phthalic acid, isophthalic acid,naphthalene-2,6-dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid,adipic acid, sebacic acid and cyclohexanediacetic acid.

The copolyesters according to the invention can be prepared in a mannerwhich is in itself known by esterifying or transesterifying thedicarboxylic acids, preferably pure terephthalic acids, and/or thecorresponding dimethyl esters with 1.05-2.4, preferably 1.1-1.4 mols ofthe diols, based on 1 mol of dicarboxylic acid component, in thepresence of esterification and/or transesterification catalysts, atbetween 150 and 250° C. (reaction step A) and polycondensing thereaction products, thus obtained, under customary conditions, that is tosay in the presence of esterification catalysts at between 200 and 300°C. under reduced pressure (< 1 mm Hg) (reaction step B).

A particularly preferred embodiment is to mix the codiol into thereaction mixture as late as possible, that is to say only after thereaction of terephthalic acid or of its ester-forming derivatives withethylene glycol to give bis(2-hydroxy-ethyl) terephthalate has takenplace or, even more advantageously, only after formation of apolyethylene terephthalate prepolymer with a degree of polycondensationof more than 4. The mixture can then be polycondensed in the customarymanner, as described above.

Both the first (A) and the second (B) step of the condensation arecarried out in the presence of catalysts, such as are described, forexample, by R. E. Wilfong in J. Polym. Sci. 54, 385 (1961). Some ofthese catalysts are more active as accelerators for the esterificationreaction A and others are more active for the polycondensation B, whilstothers again are fairly active catalysts for both reactions (C).

Catalysts which are suitable for accelerating the first reaction stage(A) include

1. lithium, sodium, potassium, calcium, strontium and boron as metals,oxides, hydrides, formates, acetates, alcoholates or glycolates;

2. the chlorides and bromides of calcium and strontium;

3. tertiary amines;

4. the malonates, adipates, benzoates and the like of calcium andstrontium; and

5. lithium salts of dithiocarbamic acids.

Suitable catalysts (B) for catalysis of the polycondensation step are,for example,

1. molybdenum, germanium, lead, tin and antimoony as metals, oxides,hydrides, formates, alcoholates or glycolates;

2. the perborates and borates of zinc and lead;

3. the succinates, butyrates, adipates or enolates of a diketone ofzinc, manganese-II, cobalt, magnesium, chromium, iron and cadmium;

4. zinc chloride and zinc bromide;

5. lanthanum dioxide and lanthanum titanate;

6. neodymium chloride;

7. mixed salts of antimony, such as, for example, potassium antimonytartrate, and salts of antimonic acids, such as potassiumpyroantimonate;

8. zinc or manganese salts of dithiocarbamic acids;

9. cobalt naphthenate;

10. titanium tetrafluoride or titanium tetrachloride;

11. alkyl ortho-titanate;

12. titanium tetrachloride-ether complexes;

13. quaternary ammonium salts which carry a titanium-hexaalkoxy radical;titanium tetraalkoxides, and alkali metal or alkaline earth metalcompounds of the alkoxides of aluminium, zirconium or titanium;

14. organic quaternary ammonium, sulphonium, phosphonium and oxoniumhydroxides and salts;

15. barium malonate, barium adipate, barium benzoate and the like;

16. the lead, zinc, cadmium or manganese salts of the monoalkyl ester ofa phenylenedicarboxylic acid;

17. antimony-catechol complexes with an aminoalcohol or with an amineand an alcohol; and

18. uranium trioxide, uranium tetrahalide, uranium nitrate, uraniumsulphate and uranium acetate.

Suitable catalysts C for accelerating both reaction steps are, forexample,

1. barium, magnesium, zinc, cadmium, aluminium, manganese and cobalt asmetals, oxides, hydrides, formates, alcoholates, glycolates andpreferably acetates;

2. aluminium chloride and aluminium bromide;

3. the succinates, butyrates, adipates or enolates of a diketone ofzinc, manganese-II, cobalt, magnesium, chromium, iron and cadmium.

Compounds which are most suitable as catalysts A are boric acid, boricacid anhydride and borates, but especially sodium acetate.

The most suitable catalysts B are the compounds of zinc, manganese,cobalt, antimony, germanium, titanium and tin, such as, for example,zinc acetate and manganese acetate, antimony trioxide, antimonytrichloride and antimony triacetate, germanium dioxide and germaniumtetrachloride and especially titanium compounds, for example tetraalkyltitanic acid esters with alkyl groups with 1-10° C. atoms, such astetraisopropyl titanate and tetrabutyl titanate.

The catalysts are employed in amounts of 0.001 to 0.2% by weight,relative to the dicarboxylic acid component (referring to the sum ofcatalysts A and B).

Thereafter inhibitors, such as are described, for example, by H.Ludewig, Polyesterfasern (Polyester Fibres) 2nd edition,Akademie-Verlag, Berlin 1974 are added in order to inhibit the catalystsafter the first reaction step is complete and in order to increase thestability of the end product. Examples of such inhibitors are phosphoricacid, phosphorous acid and the aliphatic, aromatic or araliphatic estersthereof, for example alkyl esters with 6 to 18 C atoms in the alcoholcomponent or phenyl esters, the phenyl radicals of which are optionallysubstituted by 1-3 substituents with 6 to 18 C atoms, such astrinonylphenyl phosphate, dodecylphenyl phosphate or triphenylphosphate. These inhibitors are usually employed in amounts of 0.01 to0.6% by weight, relative to the dicarboxylic acid component.

The copolyesters according to the invention should comprise polyestershaving a reduced specific viscosity (measured on a 1% strength by weightsolution in phenol/tetrachloroethane, 60 : 40, at 25° C.) of between 0.6and 2.4 dl/g, preferably between 1.0 and 1.7 dl/g. To prepare polyesterswith high reduced specific viscosities, the polyesters obtained by themelt condensation process can be subjected to further condensation insolid phase in a known manner.

For protection against thermo-oxidative degradation, the customaryamounts of stabilizers, preferably 0.001 to 0.5% by weight, relative tothe unfilled and un-reinforced copolyesters, can be added to thecopolyesters according to the invention. Examples of suitablestabilizers are phenols and phenol derivatives, preferably stericallyhindered phenols which contain alkyl substituents with 1-6 C atoms inthe two positions ortho to the phenolic hydroxyl group, amines,preferably secondary arylamines and their derivatives, phosphates andphosphites, preferably the aryl derivatives thereof, quinones, coppersalts of organic acids and compounds obtained from the addition reactionof copper-I halides with phosphites, such as, for example,4,4'-bis-(2,6-di-tert.-butylphenol),1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert.-butyl-4-hydroxybenzyl)-benzene,4,4'-butylidene-bis-(6-tert.-butyl-m-cresol),3,5-di-tert.-butyl-4-hydroxy-benzyl-phosphonic acid diethyl ester,N,N'-bis-(β-naphthyl)-p-phenylenediamine,N,N'-bis-(1-methylheptyl)-p-phenylenediamine, phenyl-β-naphthylamine,4,4'-bis-(α,α-dimethylbenzyl)-diphenylamine,1,3,5-tris-(3,5-di-tert.-butyl-4-hydroxy-hydrocinnamoyl)-hexanhydro-s-triazine,hydroquinone, p-benzoquinone, toluhydroquinone,p-tert.-butylpyrocatechol, chloranil, naphthoquinone, coppernaphthenate, copper octoate, Cu(I)Cl/triphenyl phosphite,Cu(I)Cl/trimethyl phosphite, Cu(I)Cl/trischloroethyl phosphite,Cu(I)Cl/tripropyl phosphite and p-nitrosodimethylaniline.

The flame-retarding additives which can be used for the copolyestersaccording to the invention comprise a large number of chemical compoundswhich are well known to those skilled in the art. In general, theycontain chemical elements which are used because of theirflame-retarding capacity, for example bromine, chlorine, antimony,phosphorus and nitrogen. Preferably, the flame-retarding additivesconsist of halogenated organic compounds (brominated or chlorinated),optionally as a mixture with organic or inorganic antimony compounds,for example antimony trioxide; of elementary phosphorus or phosphoruscompounds or of halogen-containing compounds as a mixture withphosphorus compounds or compounds which contain phosphorus-nitrogenbonds.

In general, the amount of flame-retarding additives will be in the rangefrom 0.5 to 50, preferably from 3 to 25 and especially from 5 to 15,parts by weight per 100 parts by weight of copolyester. Smaller amountsof compounds which contain high concentrations of the elementsresponsible for flame retardation are sufficient, for example elementaryred phosphorus is preferably used in an amount of 0.5 to 10 parts byweight per 100 parts by weight of copolyester whilst phosphorus in theform of triphenyl phosphate is used in amounts of 5 to 25 parts byweight of the phosphate per 100 parts by weight of copolyester.Halogenated aromatic compounds are employed in amounts of 2 to 20 partsby weight and substances having a synergistic action, for exampleorganic or inorganic antimony compounds, such as antimony trioxide, areused in amounts of about 1 to 10 parts by weight per 100 parts by weightof copolyester.

Halogen-containing compounds which can be used include those of theformula ##STR1## wherein n an integer from 1 to 10 and

R is an alkylene, alkylidene or cycloaliphatic radical with 1 to 20 Catoms, for example methylene,

ethylene, propylene, isopropylene, isopropylidene, butylene,isobutylene, amylene, cyclohexylene or cyclopentylidene, and

R can also denote an oxygen atom, a carbonyl group,

a sulphur atom or a sulphur-containing group, such as

a sulphoxide or sulphone group, or a carbonate group or aphosphorus-containing group,

R can also consist of two or more alkylene or alkylidene groups, whichare linked together by groups such as aromatic radicals, oxygen atoms,ester groups or carbonyl groups, sulphur atoms, sulphoxide groups orsulphone groups or phosphorus-containing groupings, and finally, R canalso be a dihydric phenol, such as bisphenol A, or a carbonate group,

Ar and Ar' are monocarbocyclic or polycarbocyclic aromatic groups, suchas phenylene, biphenylene, terphenylene, naphthylene and the like,

Y denotes organic, inorganic or organo-metallic radicals and thesubstituents represented by Y comprise (1) halogen, such as chlorine,bromine, iodine or fluorine, or (2) hydroxyl or ether groups of thegeneral formula OE,

wherein

E is a monovalent hydrocarbon radical, such as, for example, X, or (3)monovalent hydrocarbon radicals of the type represented by R, or (4)other substituents, such as nitro or cyano, the substituents mentionedbeing substantially inert and a proviso being that at least 1 andpreferably 2 halogen atoms are present per aryl nucleus,

X is a monovalent hydrocarbon group with 1 to 20 C atoms and thefollowing examples may be mentioned: alkyl, such as methyl, ethylene,propyl, isopropyl, butyl and decyl; aryl, such as phenyl, naphthyl,biphenyl, xylyl and tolyl; aralkyl, such as benzyl and ethylphenyl; andcycloaliphatic groups, such as cyclopentyl and cyclohexyl and when morethan one grouping X is present, these groups can be identical ordifferent,

the letter d in the above formula represents an integer from 1 up to themaximum equivalent of the number of replaceable hydrogens, which arebonded to the aromatic rings Ar or Ar',

the letter e represents 0 or an integer up to the maximum number ofreplaceable hydrogens on R, the letters a, b and c represent 0 or aninteger, and if b is not 0, then neither a nor c can be 0, and otherwiseeither a or c but not both can be 0, whilst if b is 0, the aromaticradicals are linked together by a direct carbon-carbon bond.

The hydroxyl and Y substituents on the aromatic radicals Ar and Ar' canbe in the ortho-, meta- or para-position on the aromatic rings and theradicals can be linked to one another in any possible way.

The following examples of diaromatic compounds fall within the scope ofthe above formula: 2,2-bis-(3,5-dichlorophenyl)-propane,bis-(2-chlorophenyl)-methane, bis-(2,6-dibromophenyl)-methane,1,1-bis-(4-iodophenyl)-ethane, 1,2-bis-(2,6-dichlorophenyl)-ethane,1,1-bis-(2-chloro-4-iodophenyl)-ethane,1,1-bis-(2-chloro-4-methylphenyl)-ethane,1,1-bis-(3,5-dichlorophenyl)-ethane,2,2-bis-(3-phenyl-4-bromophenyl)-ethane,2,3-bis-(4,6-dichloronaphthyl)-propane,2,2-bis-(2,6-dichlorophenyl)-pentane,2,2-bis-(3,5-dichlorophenyl)-hexane, bis-(4-chlorophenyl)-phenylmethane,bis-(3,5-dichlorophenyl)cyclohexylmethane,bis-(3-nitro-4-bromophenyl)-methane,bis-(4-hydroxy-2,6-dichloro-3-methoxyphenyl)-methane,2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane and2,2-bis-(3-bromo-4-hydroxyphenyl)-propane.

Substituted benzenes, such as, for example, tetrabromobenzene,hexachlorobenzene, and hexabromobenzene, and biphenyls, such as2,2'-dichlorobiphenyl, 2,4'-dibromobiphenyl, 2,4'-dichlorobiphenyl,hexabromobiphenyl, octabromobiphenyl and decabromobiphenyl, andhalogenated diphenyl ethers which contain 2 to 10 halogen atoms alsofall within the scope of the above structural formula.

The preferred halogen compounds within the scope of this invention arearomatic halogen compounds, such as chlorinated benzene, brominatedbenzene, chlorinated biphenyl, chlorinated terphenyl, brominatedbiphenyl or brominated terphenyl or a compound which comprises twophenyl radicals, which are linked together by a divalent alkylene group,and carries at least two chlorine atoms or bromine atoms per phenylnucleus.

Hexabromobenzene and brominated or chlorinated biphenyls or terphenyls,alone or as a mixture with antimony trioxide, are particularlypreferred.

In general, the preferred phosphorus compounds are selected fromelementary phosphorus or organic phosphonic acids, phosphonates,phosphinates, phosphonites, phosphinites, phosphene oxides,phosphenenes, phosphites or phosphates.

Triphenylphosphine oxide is an example of this category of compounds. Itcan be used either alone or as a mixture with hexabromobenzene or achlorinated biphenyl and optionally antimony trioxide.

Typical preferred phosphorus compounds, which can be used within thescope of the present invention, are those of the formula ##STR2## andtheir nitrogen analogues, wherein Q represents identical or differentradicals, including hydrocarbon radicals, such as alkyl, cycloalkyl,aryl, alkyl-substituted aryl and aryl-substituted alkyl; halogen,hydrogen or combinations thereof, with the proviso that at least one ofthe radicals Q is an aryl radical.

Typical examples of suitable phosphates comprise the following: phenylbis-dodecyl phosphate, phenyl bis-neopentyl phosphate, phenyl ethylenehydrogen phosphate, phenyl-bis-(3,5,5'-trimethylhexyl)phosphate, ethyldiphenyl phosphate, 2-ethylhexyl di-(p-tolyl) phosphate, diphenylhydrogen phosphate, bis-(2-ethylhexyl)-p-tolyl phosphate, tritolylphosphate, bis-(2-ethylhexyl)-phenyl phosphate, tri-(nonylphenyl)phosphate, phenyl methyl hydrogen phosphate, di-(dodecyl)-p-tolylphosphate, tricresyl phosphate, triphenyl phosphate, halogenatedtriphenyl phosphate, dibutyl phenyl phosphate, 2-chloroethyl diphenylphosphate, p-tolyl bis-(2,5,5'-trimethylhexyl) phosphate and2-ethylhexyl diphenyl phosphate.

Preferred phosphates are those in which each radical Q is of aromaticcharacter. The most preferred phosphate is triphenyl phosphate.Triphenyl phosphate is also preferably employed in a combination withhexabromobenzene and optionally antimony trioxide.

Those compounds which contain phosphorus-nitrogen bonds, such asphosphonitrile chloride, phosphorus ester amides, phosphoric acidamides, phosphonic acid amides, phosphinic acid amides,tris-(aziridinyl)-phosphine oxide ortetrakis-(hydroxymethyl)-phosphonium chloride, can also be used asflame-retarding additives.

Particularly preferred flame-retarding additives are oligomers of acarbonate of a halogenated dihydric phenol. Of these oligomers, thosewhich are preferred contain 2 to 20 recurrent units of the formula##STR3## wherein R¹ and R² are hydrogen, alkyl with 1 to 4 C atoms orphenyl,

X¹ and X² are bromine or chlorine and

m and r denote an integer from 1 to 4. These oligomeric additives have alow volatility when they are heated to temperatures above 200° C. and asoftening point of less than about 300° C. They are employed alone or incombination with substances having a synergistic action such asinorganic or organic antimony compounds.

Up to 80, preferably 10 to 40, % by weight of reinforcing materials,based on the sum of copolyester reinforcing materials, can be added tothe copolyesters according to the invention. Suitable reinforcingmaterials are fibres, whiskers or platelets of metals, for examplealuminium, iron or nickel, and non-metals, for example ceramics, carbonfilaments, silicates, asbestos, TiO₂ and titanate whiskers, quartz,glass flocks and preferably glass fibres.

Glass filaments made of calcium-aluminium-boron silicate glass, which isrelatively free from sodium carbonate, are preferably used. Glass ofthis type is known as "E" glass; however, where the electricalproperties of the reinforced copolyesters are not important, otherglasses can also be used, for example the glass with a low sodiumcarbonate content which is known as "C" glass. The diameters of thefilaments are in the range from about 0.003 to 0.018 mm, but this is notcritical for the present invention.

The length of the glass filaments and whether they have been spun togive fibres and the fibres in turn have been bundled to give yarns,ropes or hanks or woven to give mats and the like is not critical forthe invention. However, it is convenient to use fibre-like glass in theform of glass fibre staple about 3 to about 25 mm in length andpreferably less than 6 mm in length for reinforcing the copolyestersaccording to the invention. On the other hand, even shorter pieces arefound in molding produced from reinfored copolyesters according to theinvention since considerable comminution takes place during mixing. Itis, however, desirable that the lengths of the filaments are betweenabout 1.25 × 10⁻³ and about 3 mm.

Customary additives which can be used additionally in customary amountsare inert inorganic fillers, such as calcium carbonate, silicates,aluminas, lime and carbon, organic and inorganic pigments, dyestuffs,lubricants and release agents, UV absorbers and the like.

The rate of crystallization of the copolyesters according to theinvention can be further increased by adding 0.01 to 1% by weight,relative to the unfilled and unreinforced copolyesters, of nucleatingagents. Suitable nucleating agents are the compounds known to thoseskilled in the art, such as, for example, those described inKunststoff-Handbach, (Plastics Handbook), Volume VIII, "Polyester", CarlHanser Verlag, Munich 1973, page 701.

The copolyesters according to the invention can be molded at moldtemperatures between 110 and 150° C., preferably at about 120° C., andat injection pressures of 740 kp/cm² and follow-up pressures of about380 kp/cm² and, under these conditions, the cycle time can beconsiderably shorter (namely 30 to 35 seconds) than in the case ofconventional polyethylene terephthalates containing nucleating agents.As already mentioned above, the rate of crystallization can be evenfurther increased by adding nucleating agents.

The copolyesters according to the invention are excellent startingmaterials for the preparation of moldings of all types by injectionmolding.

The percentages quoted in the experiments which follow are % by weight.

EXAMPLES 1-3

97.1 g (0.5 mol) of dimethyl terephthalate are transesterified with1.045 mols of ethylene glycol in the presence of 58 mg of zinc acetatefor 2 hours at 200° C. and for 1 hour at 220° C. Whentrans-esterification is complete, 0.6 ml of GeO₂ solution (5% strengthin ethylene glycol), 103 mg of triphenyl phosphate and the correspondingcodiol are added. The temperature is raised to 250° C. in the course ofone hour and, at the same time, the apparatus is evacuated (<1.0 mm Hg).Polycondensation is complete after a further 45-60 minutes. A clearviscous melt of the copolyester is obtained and on cooling thissolidifies to a white crystalline mass.

Example 1 (Table) gives the properties of copolyesters similar to thoseof the invention, whilst Example 2 and 3 show the properties ofcopolyesters with codiol radicals which are not according to theinvention.

                                      Table                                       __________________________________________________________________________                         Amount                                                        Ethylene glycol of codiol                                                                          [η]                                                                           .increment.H.sub.m                                                                T.sub.m                                                                          .increment.H.sub.c                                                                T.sub.c                                                                          T.sub.m -T.sub.c                  Example                                                                            [mol %]**                                                                              Codiol [mol %]**                                                                          [dl/g]                                                                            [cal/g]                                                                           [° C]                                                                     [cal/g]                                                                           [° C]                                                                     [° C]                      __________________________________________________________________________    1    95      2,2-diethyl-                                                                          5    0.55                                                                              10.4                                                                              246                                                                              10.4                                                                              201                                                                              45                                             propane-1,3-diol                                                 2    95      pentane-1,5-diol                                                                      5    0.50                                                                              9.6 250                                                                              7.6 181                                                                              69                                3    95      2-ethylpropane-                                                                       5    0.52                                                                              9.8 251                                                                              7.2 178                                                                              73                                             1,3-diol                                                         __________________________________________________________________________     *After a cooling phase of 20° C/minute, the samples crystallize        again on 2nd heating.                                                         **relative to the diol component                                         

In the Table:

[η] denotes intrinsic viscosity in phenol/tetrachloroethane, 1:1,measured in a Ubbelohde capillary viscosimeter; polymer concentration:0.6 g/dl, temperature: 25° C.

Δh_(m) denotes enthalpy of melting

T_(m) denotes melting temperature

ΔH_(c) denotes enthalpy of crystallization and

T_(c) denotes crystallization temperature, measured with a DCS 2 (PerkinElmer) at a heating and cooling rate of 20° C./minute, sample weight:about 10 mg

The samples were characterized by their intrinsic viscosity and thethermodynamic data important for the melting and crystallizationproperties, such as enthalpy of metling (ΔH_(m)), melting temperature(T_(m)), enthalpy of crystallization (ΔH_(c)) and crystallizationtemperature (T_(c)).

At a constant rate of cooling and under otherwise identical experimentalconditions, the rate of crystallization is higher the earlier thepolymer crystallizes out, that is to say the super-cooling: ΔT = T_(m) -T_(c) indicates when the rate of crystallization reaches its maximumunder the cooling conditions used.

We claim: Patent Claim:
 1. Molded articles of highly crystalline,thermoplastic terephthalic acid copolyesters which crystallize rapidlyand which consist of at least 90 mol %, relative to the dicarboxylicacid component, of terephthalic acid radicals, 95.2 to 99.5 mol %,relative to the diol component, of ethylene glycol radicals and 0.5 to4.8 mol %, relative to the diol component, of 2.2-diethylpropane-1.3-diol radicals.